Reverse DNS Lookup
Reverse DNS maps an IP address back to a hostname through a PTR record set by whoever controls the address block — usually the ISP or hosting company. It is how mail servers and log tools put a name to a number.
Why does an IP have no reverse DNS?
PTR records are optional. Many residential and mobile IPs have generic ones or none at all. Mail servers are the exception — sending mail without matching forward and reverse DNS gets flagged as spam.
What can a hostname tell me?
ISP hostnames often encode the provider and rough region. A hostname like static.55.100.x.x.clients.example-host.com tells you it is a hosting company's machine rather than a home connection.
This tool also lives in the homepage tool drawer alongside 17 others. Browse everything on the tools page or look up any address with the IP lookup.